SOIL SAMPLING OF MANURED AND NON - MANURED FIELDS IN GRASS FORAGE PRODUCTION

Transcription

1 SOIL SAMPLING OF MANURED AND NON - MANURED FIELDS IN GRASS FORAGE PRODUCTION Presented To Manitoba Livestock Manure Management Initiative Inc. By L. Slevinsky, P. Ag., CAC Dr. D. Lobb, PhD. E. St. Jacques July,

2 TABLE OF CONTENTS Acknowledgements 1 Executive Summary Introduction Project Objectives Methodology Site Selection Soil Sampling Soil Analysis Field Histories Grass Forage Species Data Analysis and Interpretation Results Soil Description of Sampling Locations Plant Species Water Table Depth Field Histories Soil Nitrogen and phosphorus Discussion Nitrogen and Phosphorous Variability Do Fields with a History of Manure Application Differ in Fertility Status from Those Without? Are There Differences In Fertility Status Between the Manured Sites? Are There Differences In Fertility Status Between the Non-Manured Sites? Is There a Relationship Between Nutrient Status and Depth Within the Soil Profile?..17 2

3 5.6 Is There Evidence of Nutrient Leaching on Manured Sites Sites? Is There Increased Potential for Nutrient Runoff on Manured Sites? How Many Soil Samples are Required to Accurately Estimate the Average Nutrient Status of Fields With and Without a History of Manure Application? Does the Method of Sample Collection Affect the Estimate of the Average Nutrient Status of Fields? Conclusions Recommendations for Future Studies References 23 3

4 LIST OF APPENDICES Appendix A: Appendix B: Appendix C: Appendix D: Enviro Test Laboratories Soil Test Recommendations Enviro Test Laboratories Test Methodologies Soil Attributes and Nitrate Nitrogen Phosphorus Tables Benchmark Attributes and Nitrogen - Phosphorus Tables Appendix E: Field History Tables Appendix F: Appendix G: Appendix H: Appendix I: Appendix J: Appendix K: Appendix L: Statistical Analysis of Fertility Status Between Manured and Non-Manured Sites Statistical Analysis of Fertility Status Between Manured Sites Statistical Analysis of Fertility Status Between Non- Manured Sites Statistical Analysis of Nutrient Status and Depth Within the Soil Profile for Manured Sites Statistical Analysis of Nutrient Status and Depth Within the Soil Profile for Non-Manured Sites Graphs of Nitrate Concentration With Depth Graphs of Phosphorus Concentration With Depth 4

5 ACKNOWLEDGEMENTS The authors would like to express their gratitude to the following organizations for the funding assistance provided during the course of this study: Manitoba Livestock Manure Management Initiative, Manitoba Pork Council, Elite Swine Inc., Hytek Feed Co-operative Ltd., Puratone Corporation, Hart Feeds, SPADA and PFRA. The co-operation and assistance of the producers that made their lands available for soil sampling is very much appreciated. In addition we also gratefully acknowledged the Remote Sensing Centre and Manitoba Conservation for their co-operation and assistance in the use of aerial photography, and Enviro-Test Laboratories for their analysis of the soil samples. 5

6 EXECUTIVE SUMMARY This survey study was initiated to investigate the nutrient status of agricultural soils in South Eastern Manitoba that have a history of hog manure application and to compare these soils to similar soils that have not received manure. The land areas that were studied were characterized by coarse textured, low agricultural capability soils in grass forage production. The study locations would be considered representative of soil landscapes commonly known as the Poppleton, Pelan and Malonton soil associations. The variability in soil nitrate nitrogen and phosphorus with depth was determined at twelve manured locations and six non-manured locations each about eighty acres in area. Three soil-sampling procedures were conducted at each field location. The first consisted of individually sampling fifteen randomly selected sites identified with global positioning coordinates. The second involved taking a sub-sample from each of these fifteen sites for a single composite sample. The third procedure consisted of selecting, at the investigator s discretion, four of the random sites to represent the whole field (benchmark sampling). The study found that there was a higher concentration of nitrogen and phosphorus to a depth of sixty centimeters in manured fields, especially for phosphorus when compared to non-manured fields. However, at some of the non-manured sites there was evidence of elevated nitrogen and phosphorus levels that were lower than the manured sites. The importance of keeping good production records of cultural, nutrient and manure management practices are essential in providing information for relating residual nutrient levels to nutrient balances of applied organic and inorganic fertilizers. The data showed that the variability in nitrate nitrogen and phosphorus status was greater between fields than within fields, particularly for nitrogen status whether the fields were manured or non-manured. The highest concentrations of nitrogen and phosphorous were found at the soil surface (0-15 cm) with nutrient levels decreasing with depth. In some cases concentrations of nitrogen and phosphorus were observed below the 0 15 cm depth and in some cases they were not. Deep sampling also showed concentration of nutrients below 60 cm in some cases. As with any addition of nutrients there are potential risks to runoff and surface water contamination or leaching and groundwater contamination. The method of sample collection did not affect the assessment of nitrate nitrogen and phosphorus status for fields. There was no difference in sampling accuracy between the analyses of fifteen individual samples for a field site and the analyses of the single composite of the fifteen individual samples. Nor were there 6

7 any differences between the composite sample and the expert sampling method (four benchmark sample sites per field). It was determined that a lesser number of samples is required for determining the nitrogen status than the phosphorus status for manured fields. As for nonmanured locations generally a lesser number and the same number of samples were required for determining the nitrogen and phosphorus fertility status of fields. Water table depths were found to vary more between locations than within each location. At the manured locations water table depths ranged from one to two feet to greater than nine feet. Depth to water table at the non-manured locations ranged from two to three feet to greater than nine feet from the ground surface. The dominant grass forage species identified at the majority of the soil sampling sites were quack grass and poa with quack grass being more prevalent than poa at most field locations 7

8 1.0 INTRODUCTION In South Eastern Manitoba there exists a considerable number of intensive hog operations. The manure produced from these operations is being applied in many cases to lands characterized by coarse textured, low agricultural capability soils in grass forage production. Soil types within these lands have textures ranging from loamy sand to sand to sand with gravel with depth and are usually underlain by loamy till or stratified coarse material deposits. Because of their sandy textures these soils have high permeability, low water holding capacity and the high potential for leaching. The presence of materials with low permeability underlying the sandier surface materials can result in perched water tables in the spring or during intensive rainfall events during the growing season. Lands characterized by these soil conditions are considered to be sensitive and are subject to a limit of 60 pounds of nitrogen per acre from hog manure to estalblished grass forage stands. The present application restraint of 60 pounds per acre is less than the agronomic nitrogen rate to produce a target forage yield of 3 ton per acre. Enviro - Test Laboratories nitrogen fertility recommendation for a 3 ton per acre grass hay forage with moderate levels of residual nitrogen is 90 to 100 pounds per acre (see Table A1, Appendix A). For a forage crop with a mixture of 50 percent grass / 50 percent alfalfa the recommendation is 85 to 95 pounds per acre (see Table A2, Appendix A). Computed average nitrogen uptake values for a grass forage and a 50 percent grass / 50 percent alfalfa forage from data compiled by the Canadian Fertilizer Institute (1998) were determined to be 34 and 46 pounds per acre respectively for each ton of dry matter. Forage yields of 4 ton per acre have been observed in this region. At present there is limited information regarding the nitrogen and phosphorus levels in the soils of the sensitive lands in South Eastern Manitoba. Under existing manure nutrient management practices there is a need: a) to determine the concentration and variability with depth of the nitrogen and phosphorus in manured and non-manured fields in South Eastern Manitoba: and b) to determine whether the nitrogen application limit of 60 pounds per acre is warranted, and whether phosphorus levels are an issue in these forage lands where hog manure is being applied. In order to determine the concentration and variability of nitrogen and phosphorus in these sensitive lands a sampling survey was undertaken. 8

9 2.0 PROJECT OBJECTIVES The objectives of this study were to determine: The variability in soil nitrate-nitrogen and available phosphorus levels in manured and non-manured fields in grass forage production. The concentration of nitrate-nitrogen and available phosphorus over the depth of the soil profile in manured and non-manured grass forage fields characterized with coarse textures. Whether a composite soil sample from fifteen randomly selected sites within a field is an accurate method for assessing soil nutrient levels in manured and non- manured fields in grass forage production. Whether benchmark sampling of four locations is an accurate method for assessing soil nutrient levels in manured and non-manured fields in grass forage production. The depth to water table at four benchmark sites at selected field locations in grass forage production. The concentration of nitrate-nitrogen and available phosphorus at four benchmark sites at selected field locations in grass forage production to the perched water table depth. The history of the nutrient and manure management practices for selected field locations in grass forage production. The dominant grass forage species at each randomly selected sampling site at selected field locations. 9

10 3.0 METHODOLOGY 3.1 Site Selection A total of eighteen fields, approximately eighty acres in area, were soil sampled in October All of the selected fields are characterized by coarse textured soils. Twelve of these fields are manured and six are non-manured. All manured fields received at least one year of application in the past three years with some being manured more frequently. Not all of the manured fields received manure in the fall of All the manure applied to the manured fields was from hog operations. As of the fall of 2001 all fields were predominantly in grass forages. 3.2 Soil Sampling Field Locations At each field location three sampling procedures were conducted for comparison. Using aerial photos, each field was stratified into about eighty one-acre units for sampling. The first procedure consisted of sampling fifteen randomly selected sites. Each sampling site was georeferenced with GPS (global position system). The second procedure consisted of taking a subsample from each of the randomly selected sites to form a composite sample, and the third consisted of selecting, at the investigators discretion, four of the random sites to represent the whole field, i.e. benchmark sites. In all field locations and at each sampling site soil samples were taken at the 0 to 15, 15 to 30 and 30 to 60 cm depths. The number of soil samples taken at each field location was 48 (15 sites x three depths plus one composite sample x three depths). The number of individual samples taken was 810 plus 54 composite samples, equaling 864 samples Benchmark Sites At each benchmark site for each field location (except M11) soil samples were taken at one-foot (30cm) increments until the perched water table was reached. The depth to water table for each benchmark site was documented. The total number of samples taken for all locations was Soil Analysis All soil samples were analyzed for nitrate-nitrogen and available phosphorus. Enviro Test Laboratories located in Winnipeg, Manitoba tested the samples. The method used for nitrate-nitrogen extraction was CaCl 2. Available phosphorus was extracted using NaHCO 3 (Olson method). The laboratory test methodologies are attached in Appendix B. 10

11 3.4 Field Histories Field history information was obtained by interviews and discussions with industry, government personnel and producer co-operators. The following information was collected for each field location: crop, yield, manure analysis, time and method of manure application, manure application rate and inorganic fertilizer use and rate. Values for nitrogen application rate, total phosphorus applied, and nitrogen and phosphorus uptake were determined. The nitrogen and phosphorus uptake values were estimated using average values from data compiled by the Canadian Fertilizer Institute (1998) for forage crops on a dry matter basies. 3.5 Grass Forage Species The dominant grass forage species at each sampling site at each field location was determined and recorded. Plant species were determined through visual identification by the investigator in an area of approximately one square meter. 3.6 Data Analysis and Interpretation An analysis of the data was conducted to address the following questions: Do fields with a history of manure application differ in fertility status from those without? Are there differences in fertility status between the manured sites? Are there differences in fertility status between the non-manured sites? Is there a relationship between nutrient status and depth within the soil profile? Is there evidence of nutrients leaching on manured sites? Is there increased potential for nutrient runoff on manured sites? How many soil samples are required to accurately represent the fertility status of fields with and without a history of manure application? Does the method of sample collection affect the assessment of nitrogen and phosphorus status for fields? Statistical analyses were carried out on log-transformed data using Analysis of Variance (ANOVA) with JMP IN version 3.2 software published by the SAS Institute. 11

12 The majority of the data were not normally distributed: that is in each sample population a few large samples skewed the data, Consequently, in order to fulfill the assumptions of ANOVA, the analyses were conducted on log-transformed data. In all comparisons a 95 % confidence limit was used. Differences are indicated by Yes (P<0.05); No (P>0.10); or Maybe (0.10<P>0.05). Interpretation of depth-concentration data was carried out using graphs generated in MS- EXCEL. 12

13 4.0 RESULTS 4.1 Soil Description of Sampling Locations The soil series varied from field location to field location and varied within individual field locations due to variability in parent material, topography and drainage. At the sampling sites the dominant profile textures to two feet ranged from sands to loamy sands with areas of sand and gravel. Drainage ranged from well to poor with the majority of the field locations being imperfectly drained. With the exception of M1 the field locations were characterized by level landscapes with slope percentages of less than two percent. At all locations the soils were non-saline and non-stony (except NM1). The carbonate levels in the soil profile within two feet from the ground surface ranged from none to high. A more detailed description of the sampling locations is presented in the table found in Appendix C. 4.2 Plant Species The dominant forage species identified at the majority of the soil sampling sites were quack grass and poa with quack grass being more prevalent than poa at most field locations. Other grass species identified at some of the sampling locations were orchard and timothy. A detailed listing of the plant species found at each of the sampling sites at each field location appears in Appendix C. Very little alfalfa was observed at the time of sampling, and those areas that had alfalfa were not sampled. 4.3 Water Table Depth Water table depths at the benchmark sites appear to vary more between locations than within each field location. Depth to water table at the non-manured locations ranged from 2 to 3 feet (NM1) to greater than nine feet (NM3) from the ground surface. At the manured locations water table depths ranged from one to two feet (M7) to greater than nine feet (M5). In general, water table depths were found to be closer to the soil surface where the coarser textured materials (sandy) were underlain by finer materials of till or clay. At some of the benchmark sites where finer textured materials occurred with depth throughout the soil profile the water table levels occurred at lower depths. The same was true at some benchmark locations characterized by greater depths of coarse textured materials. A more detailed documentation of water table depths at each benchmark site for each field location is given in Appendix D. 4.4 Field Histories As stated above, field locations are cropped with grass forage. Prior to 2001 all fields were approximately in a fifty percent grass / fifty percent alfalfa mixture. The dominant method of manure application is broadcasting by tanker with a 13

14 dribble bar or splash plate (see Appendix E). Typically, manure is applied to these lands in the summer or in the fall of the year; however, some of the manured fields did not receive manure prior to sampling in the fall of Application rates of manure varied from year to year at some of the field locations and were similar at other locations from one year to the next. Manure analysis for ammonium-nitrogen and total phosphorus varied considerably from one location to the other(see Appendix E). Based on field records, no inorganic fertilizer was applied to any of the manured fields. Forage yields varied from one location to the other and also between years for most of the field locations. From the historical data collected there were nine instances were the nitrogen uptake by the forage crop is estimated to be greater than the amount of nitrogen applied to the crop, twelve cases where the reverse was true and two instances where the amount of nitrogen applied was pretty well equal to the amount utilized by the crop. At all the manured field locations the amount of phosphorus applied was much greater than the amount of phosphorus that was estimated to be removed by the forage crops, given the yields that were reported for all fields. Nitrogen and phosphorus uptake and removal is dependent upon the crop yield, whereas manure nitrogen and phosphorous applied is dependent on the concentration of the nitrogen and phosphorus in the manure, the method of application and the rate of application. Based on the field histories that were obtained, all non manured fields with the exception of NM4 did not receive any applications of inorganic fertilizers. The non-fertilized fields had similar forage yields (1.4 ton per acre) that were significantly less than the forage yields (alfalfa/grass) recorded (4.6 ton per acre) for NM4. In Appendix E, a more detailed listing of the documented nutrient and manure management practices for the twelve-manured fields and four of the nonmanured fields are provided. 4.5 Soil Nitrogen and Phosphorus The nitrogen and phosphorus concentrations for all 864 soil samples: individual sample site, composite and bench mark values for each manured and non - manured location at the 0 15, and cm depths are presented in Appendix C. In Appendix D, the nitrogen and phosphorus concentrations for all 463 samples representing the deeper sampling at all benchmark sites for each field location (except M 11) are listed. A summary of the data and basic descriptive statistics for each field site sampled are provided in Table 1. This table illustrates the general fertility status of the soil profile (0 15, and cm depths) for manured and non-manured sites. Given that the data is not normally distributed, the median values, not the 14

15 mean values, should be used to assess the probability of finding a fertility level, i.e. the central tendency of the sample data. General statistical results from the ANOVA are provided in Appendix F; detailed statistical results are provided in Appendices G through K. Graphs of the depthconcentration data are found in Appendix L and M. 15

16 Manured Non- Manured Table 1. Summary of Data. N* 0-15** N Mean N P 0-15 P P N 0-15 N Median N P 0-15 P P N 0-15 Standard Deviation M M M M M M M M M M M M NM NM ,1 NM NM NM ,2 0, NM * N denotes nitrate nitrogen ** Numerical values in cm N N P 0-15 P P N 0-15 N N Max P 0-15 P P

17 5.0 DISCUSSION 5.1 Nitrogen and Phosphorus Variability Table 1 demonstrates that there was a high degree of variability within and between field locations, as indicated by the large standard deviations and ranges. These results are similar to the findings found in a preceding study of annual croplands (Slevinsky et al., 2001). There are a number of causes of such variability. One possible cause is the variability in nutrient concentration of the hog manure within the storage facility (earthen manure storages). Another possible cause is the variability in application due to the method of application. 5.2 Do Fields with a History of Manure Application Differ in Fertility Status from Those Without? The data in Table 2 reveals that the manured fields were higher in nitrogen and phosphorus status over the entire depth of the soil profile to a depth of 60 cm. This was particularly true for phosphorus status (Appendix F). Table 2. Comparison of Manured and Non-Manured Sites* N 0-15 cm N cm N cm P 0-15 cm P15-30 cm P cm Manured Non Manured Different? Yes Yes Yes Yes Yes Yes *Note: Data shown are sample medians (reported differences are based on log-transformed data) 5.3 Are There Differences in Fertility Status Between the Manured Sites? The information presented in Tables 3a to 3f indicates there are differences in fertility status between the manured locations. The variability in nitrogen and phosphorus status between manured fields is greater than the variability within manured fields, particularly for nitrogen status (Appendix G). Table 3 provides the comparison of manured sites for nitrogen and phosphorus for each of the three sampling depths. Many more differences exist for nitrogen than phosphorous. Due to inherent field conditions and management histories, each field should be considered unique. Consequently, nutrient management planning for manured fields should be carried out on a field-by-field basis. It may be possible, after tracking fertility status over the years, to group fields for the purposes of nutrient 17

18 management planning. However, it is also possible, given the variability within fields, that individual fields should be segmented into management zones for the purposes of nutrient management planning. Table 3a. Comparison of Manured Sites: Nitrogen 0-15 cm M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M1 * * * * M2 * * * * * * * * * * M3 * * * * * * * * M4 * * * * * * * M5 * * * * * * * * * M6 * * * * M7 * * * * * M8 * * * * * M9 * * * * * * * * * M10 * * * * * M11 * * * * M12 * * * * * indicates significant difference using Tukey-Kramer HSD. Table 3b. Comparison of Manured Sites: Nitrogen cm M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M1 * * * * * M2 * * * * * M3 * * * * M4 * * * * * * M5 * * * * * * * * * * M6 * * * M7 * * * * * M8 * * * M9 * * * * * * * * M10 * * M11 * * M12 * * * * * * indicates significant difference using Tukey-Kramer HSD. Table 3c. Comparison of Manured Sites: Nitrogen cm M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M1 * * * * * M2 * * * * * M3 * * * * M4 * * * * * * * * M5 * * * * * * * * * M6 * * * * M7 * * * * * * * M8 * * * M9 * * * * * * M10 * * * * * M11 * * * * M12 * * * * * * 18

19 * indicates significant difference using Tukey-Kramer HSD. Table 3d. Comparison of Manured Sites: Phosphorus 0-15 cm M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M1 * * * M2 * * * * * * * M3 * M4 * M5 * * M6 * * M7 * * * M8 * * M9 * * * M10 * * * * * * * * M11 * * M12 * * * * * indicates significant difference using Tukey-Kramer HSD. Table 3e. Comparison of Manured Sites: Phosphorus cm M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M1 * * * * * * M2 * * M3 * M4 * M5 * M6 M7 * * M8 * M9 M10 * * * M11 M12 * * * * indicates significant difference using Tukey-Kramer HSD. Table 3f. Comparison of Manured Sites: Phosphorus cm M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M1 * * * * * * * * * M2 * * * M3 * * * M4 * * * M5 * M6 * M7 * * * M8 * M9 * M10 * * * * * M11 * * * * M12 * * * indicates significant difference using Tukey-Kramer HSD 5.4 Are There Differences in Fertility Status Between the Non-Manured Sites? 19

20 As with the manured sites, the variability between fields is greater than the variability within fields, particularly for nitrogen status (Appendix H). Table 4 provides the comparison of non-manured sites for nitrogen and phosphorus for each of the three sampling depths. Many more differences were observed for nitrogen than phosphorus. Although it was presumed that nutrients had not been applied to the nonmanured locations except NM4, the elevated nitrogen and phosphorus levels at some indicate a history of some form of nutrient application. As stated for the manured sites, due to inherent field conditions and management histories, each field should be considered unique. Table 4a. Comparison of Non-Manured Sites: Nitrogen 0-15 cm NM1 NM2 NM3 NM4 NM5 NM6 NM1 * * NM2 * * NM3 * NM4 * * * * * NM5 * * NM6 * * * * * indicates significant difference using Tukey-Kramer HSD. Table 4b. Comparison of Non-Manured Sites: Nitrogen cm NM1 NM2 NM3 NM4 NM5 NM6. NM1 * * NM2 * * NM3 * NM4 * * * * NM5 * * * NM6 * * * indicates significant difference using Tukey-Kramer HSD. Table 4c. Comparison of Non-Manured Sites: Nitrogen cm NM1 NM2 NM3 NM4 NM5 NM6 NM1 * * * * NM2 * * * NM3 * * * NM4 * * * NM5 * * NM6 * * * * indicates significant difference using Tukey-Kramer HSD. Table 4d. Comparison of Non-Manured Sites: Phosphorus 0-15 cm NM1 NM2 NM3 NM4 NM5 NM6 20

21 NM1 NM2 * NM3 * NM4 * * NM5 NM6 * indicates significant difference using Tukey-Kramer HSD Table 4e. Comparison of Non-Manured Sites: Phosphorus cm NM1 NM2 NM3 NM4 NM5 NM6 NM1 * NM2 * * * * NM3 NM4 * NM5 * NM6 * * indicates significant difference using Tukey-Kramer HSD. Table 4f. Comparison of Non-Manured Sites: Phosphorus cm NM1 NM2 NM3 NM4 NM5 NM6 NM1 * NM2 * * * NM3 * NM4 * NM5 * NM6 * * * * indicates significant difference using Tukey-Kramer HSD. 5.5 Is There a Relationship Between Nutrient Status and Depth Within the Soil Profile? For data from both the standard sampling and the deep sampling on the benchmark sites, nitrogen and phosphorus are often concentrated at the soil surface (0 15 cm) and decrease in concentration with depth. However, in some cases, maximum concentrations were measured below the surface. The statistical analysis indicated an interaction between site and sampling depth; consequently it is necessary to examine each site independently (Appendix I and J). 5.6 Is There Evidence of Nutrient Leaching on Manured Sites? Concentrations of nitrogen and phosphorus that were obviously elevated by comparison to the non-manured data, below the 0-15 cm sampling depth were interpreted as evidence of nutrient leaching. In most cases elevated concentrations of nitrogen and phosphorus were observed below the 0-15cm depth, but in some cases they were not. The fact that nitrogen and phosphorus 21

22 were found at depth indicates the movement of nutrients and the potential for groundwater contamination. It is difficult to assess the degree of leaching because only one sampling point in time was taken and the period between manure application and sampling was as much as one year. In 2001 eight of the twelve manured fields had received manure applications. In five of these fields the manure was applied in the fall (September or October) while in the remaining three fields the manure was applied during the summer (July). It is possible that some nutrients have leached below the 60 cm depth between manure application and sampling. It is also possible that nitrogen was denitrified during that same period. Deep sampling at the benchmark sites reinforces the findings of the standard depth sampling. There is evidence of nutrient movement at many, but not all field locations. Selected depth profiles of nitrogen and phosphorus concentrations are provided in Appendix K and L. 5.7 Is There Increased Potential for Nutrient Runoff on Manured Sites? Elevated concentrations of nitrogen and phosphorus at the soil surface increase the potential for nitrogen and phosphorus runoff associated with the runoff of water (surface and shallow-subsurface) and with soil eroded by surface water runoff; consequently, there is an increased potential for surface water contamination. The same situation exists, to a lesser degree, with the nonmanured sites. It should be noted that no evidence of runoff or soil erosion were observed. This is largely due to the fact that these fields are characterized by relatively flat, coarse textured soils, cropped with permanent forages. 5.8 How Many Soil Samples are Required to Accurately Estimate the Average Nutrient Status of Fields With and Without a History of Manure Application? Table 5 indicates the number of samples required to be within five ppm of the actual field value with ninety percent confidence. Where nutrient concentrations are higher and more variable, more samples are required to achieve this level of precision and accuracy. Fewer samples are required for the nitrogen status of manured fields than the phosphorus status (similar results to a preceding study on annual croplands, Slevinsky et al., 2001). For non-manured fields the same number of samples were required for determining the nitrogen or phosphorus fertility status of the fields. Accepting a seventy five percent confidence rather than a ninety percent confidence, or an error of ten ppm rather than five ppm, can reduce the numbers in Table 5. Table 5. Comparison of Sample Numbers* N 0-15 cm N 15-30cm N cm P 0-15 cm P cm P cm 22

23 Manured Non-Manured * Note: based on the variance of the 15 stratified-random samples collected at each site. 5.9 Does the Method of Sample Collection Affect the Estimate of the Average Nutrient Status of Fields? In Table 6 the results shows that for any given field location, there are no significant differences between the laboratory analyses of fifteen individual samples for a field site and the analyses of the single composite of the fifteen individual samples. This result is similar to the one found in an earlier study on annual croplands (Slevinsky et al., 2001). Nor were there any differences between the composite sample and the expert sampling method (the laboratory analyses of the four benchmark samples per field). Only one difference was noted and that was between the mean of the fifteen individual samples and the expert sampling method for phosphorus at cm depth. The results presented above, however, are very dependent on the skill and expertise of the person conducting the soil sample collection and handling. More specifically, the ability to stratify and randomly select sampling sites, the ability to prepare accurate composite samples and the ability of the person to select benchmark sites which represent the field site. Table 6. Comparison of Sampling Methods* N 0-15 cm N 15-30cm N cm P 0-15 cm P cm P cm Manured Multiple Samples Composite Samples Different? No No No No No No Multiples Samples Expert Samples Different? No No No No No No Composite Samples Expert Samples Different? No No No No No No Non-Manured Multiple Samples Composite Samples Different? No No No No No No Multiples Samples Expert Samples Different? No No No No No Yes Composite Samples Expert Samples Different? No No No No No No 23

24 * Note: Data shown are sample means. Comparisons were carried out on the differences between values for individual field sites (paired two-tailed t-test). 24

25 6.0 CONCLUSIONS The following is a summary of relevant findings: Manured fields were higher than non-manured fields in nitrate-nitrogen and phosphorus status over the entire depth of the soil profile to a depth of 60 cm. The variability in nitrate-nitrogen and phosphorus status was greater between fields than within fields, particularly for nitrogen status whether the fields were manured or non-manured. Typically, the highest concentrations of nitrate-nitrogen and phosphorus were found at the soil surface (0-15 cm) and decreased in concentration with depth. As with any addition of nutrients there are potential risks to runoff and surface water contamination or leaching and groundwater contamination. Soluble nutrients that are in excess of crop requirements present a greater risk of being transported to water through runoff or leaching, particularly where the soil types are characterized by coarse textures and rapid permeability. Method of sample collection did not affect the assessment of nitratenitrogen and phosphorus status for fields. There were no significant differences between the analyses of 15 individual samples for a field site and the analyses of the single composite of the 15 individual samples. Nor were there any differences between the composite sample and the expert sampling method (4 benchmark sample sites per field). To determine the nutrient status of a field within 5 ppm with a 90 percent confidence, a lesser number of samples are required for determining the nitrogen status than the phosphorus status for manured fields. As for nonmanured fields, the same number of samples was required for determining the nitrogen and phosphorus fertility status of fields. For nitrogen at the 0-15 cm depth and at all depths for phosphorus a lesser number of samples was required compared to the manured sites. 25

26 7.0 RECOMMENDATIONS for FUTURE STUDIES Based on the documented field histories of nitrogen application and nitrogen removal there should not be significant accumulation of nitrogen in the soil and therefore no significant losses to the environment through leaching and runoff. However, there was evidence of nitrogen accumulation and evidence of leaching. Additional research/monitoring is required to determine the appropriateness of the 60-pound per acre rate. Nitrogen and phosphorus balance studies need to be conducted at several of the selected locations investigated in this study to include crop use and removal, climate conditions, manure storage, handling (separate the liquid and solid phases) and application techniques. 26

27 8.0 REFERENCES Canadian Fertilizer Institute Nutrient Uptake and Removal by Field Crops Enviro Test Laboratories Soil Test Recommendations for Forage Crops. Slevinsky, L., D. Lobb and D. Small Soil Sampling of Manured and Non- Manured Fields. A report presented to the Manitoba Livestock Management Initiative Inc. 27

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